A general overview of the role of glycine transporter-1 (GlyT1) inhibitors for the treatment of diseases can be taken for example from WO2010/086251. This role of glycine transporter-1 (GlyT1) inhibitors is applicable for the present invention.
Schizophrenia is a progressive and devastating psychiatric disease characterized by episodic positive symptoms such as delusions, hallucinations, thought disorders and psychosis and persistent negative symptoms such as flattened affect, impaired attention and social withdrawal, and cognitive impairments (Lewis D A and Lieberman J A, 2000, Neuron, 28: 325-33). For decades research has focused on the “dopaminergic hyperactivity” hypothesis which has led to therapeutic interventions involving blockade of the dopaminergic system (Vandenberg R J and Aubrey K R., 2001, Exp. Opin. Ther. Targets, 5(4): 507-518; Nakazato A and Okuyama S, et al., 2000, Exp. Opin. Ther. Patents, 10(1): 75-98). However, this pharmacological approach does not effectively treat negative and cognitive symptoms which are the best predictors of functional outcome (Sharma T., 1999, Br. J. Psychiatry, 174(suppl. 28):44-51).
A complementary model of schizophrenia was proposed in the mid-1960′ based upon the psychotomimetic action caused by the blockade of the glutamate system by compounds like phencyclidine (PCP) and related agents (e.g. ketamine) which are non-competitive antagonists of the glutamate N-methyl-D-aspartate (NMDA) receptor. Interestingly in healthy volunteers, PCP-induced psychotomimetic action incorporates positive and negative symptoms as well as cognitive dysfunction, thus closely resembling schizophrenia in patients (Javitt D C et al., 1999, Biol. Psychiatry, 45:668-679; see also Jentsch and Roth, 1999, Neuropsychopharmacology 20:201-225. Therefore, increasing NMDA-receptor neurotransmission in the central nervous system offers an opportunity for the development of novel treatment approaches for schizophrenia and also other neurological and psychiatric diseases related to NMDA-receptor and/or glutamatergic dysfunction. The NMDA-receptor is a ligand-gated ion channel composed of a combination of two NR1 and two NR2 subunits and requires the concomitant binding of glutamate at the NR2 subunit and glycine as a co-agonist at the NR1 subunit to be activated (Johnson and Ascher, 1987, Nature 325:529-531). While glutamate is released in an activity-dependent manner from synaptic terminals, glycine is apparently present at a more constant level and seems to modulate/control the receptor for its response to glutamate. One of the most effective ways to control synaptic concentrations of neurotransmitter is to influence their re-uptake at the synapses. In forebrain areas like prefrontal and frontal cortex, hippocampus, striatum and thalamus, glycine has been shown to be necessary for glutamatergic NMDA-receptor activity and to modulate NMDA-receptor dependent excitatory neurotransmission (Johnson and Ascher, 1987, Nature 325: 529-531; Danysz and Parsons, 1998, Pharmacol. Rev. 50: 597-664). The ability of glycine to modulate NMDA-receptor mediated neurotransmission suggests that pharmacological manipulation of synaptic glycine could prove effective in the treatment of conditions involving a hypofunction of the NMDA-receptor such as schizophrenia. Thus, one strategy to enhance NMDA receptor activity is to elevate the glycine concentration in the local microenvironment of synaptic NMDA receptors by inhibition of GlyT1 (Bergeron R. et al., 1998, Proc. Natl. Acad. Sci. USA 95:15730-15734). In fact, clinical studies with direct glycine site agonists D-serine and a prototype GlyT1-inhibitor, sarcosine, which increases glycine in the synaptic cleft, have demonstrated some efficacy for the treatment of negative symptoms and to a lesser extent, positive and cognitive symptoms of schizophrenia (Tsai et al., 2004, Biol. Psychiatry 44:1081-1089; Lane et al., 2005, Biol. Psychiatry 63:9-12). Recently, clinical efficacy regarding negative symptoms in schizophrenia patients was reported for the GlyT1-inhibitor RG1678 tested in a clinical phase II trial as adjunctive treatment to marketed antipsychotics (Umbricht et al., 2011, Schizophr. Bull. 37(Supp1.1):324).
Efficacy in various animal models/tests for positive and negative symptoms of schizophrenia as well as in several memory tasks has been reported in the literature for different GlyT1-inhibitors. In detail, the selective GlyT1-inhibitors SSR504734 and SSR103800 were shown to be efficacious in two models for antipsychotic activity, i.e. reversal of NMDA-receptor antagonist induced hyperlocomotion and pre-pulse-inhibition, well known models for positive symptoms of schizophrenia (Depoortere et al., 2005, Neuropsychopharmacology 30:1963-1985; Boulay et al., 2008, Pharmacol. Biochem. Behav. 91:47-58). Regarding negative symptoms, SSR504734 was demonstrated to increase dopamine in the prefrontal cortex, a mechanistic in-vivo model for negative symptoms in schizophrenia (Depoortere et al., 2005, Neuropsychopharmacology 30:1963-1985). Regarding memory enhancement, both GlyT1-inhibitors were efficacious in the social recognition test (Depoortere et al., 2005, Neuropsychopharmacology 30:1963-1985; Boulay et al., 2008, Pharmacol. Biochem. Behav. 91:47-58). Another GlyT1-inhibitor, NFPS, was shown to be active in the object recognition and social recognition test regarding reversal of MK-801-induced cognitive deficits (Karasawa et al., 2008, Behav. Brain Res. 186:78-83; Shimazaki et al., 2010, Psychopharmacology 209:263-270). In addition, an enhancing effect on long-term potentiation in hippocampal slices could be shown with NIPS demonstrating that inhibition of GlyT1 leads to strengthening of synaptic plasticity which is crucial for memory formation on a cellular level (Kinney et al., 2003, J. Neurosci. 23:7586-7591). In fact, glutamate neurotransmission, in particular NMDA receptor activity, plays a critical role in synaptic plasticity, learning and memory, such as the NMDA receptors appears to serve as a graded switch for gating the threshold of synaptic plasticity and memory formation (Bliss T V and Collingridge G L, 1993, Nature, 361:31-39).
In addition, GlyT1-inhibitors were shown to be efficacious in animal models of depression, anxiety and sleep, such as chronic mild stress, ultrasonic distress calls in rat pups and increased latency of paradoxical sleep (Depoortere et al., 2005, Neuropsychopharmacology 30:1963-1985).
Two distinct glycine transporter genes have been cloned (GlyT1 and GlyT2) from mammalian brain, which give rise to two transporters with −50% amino acid sequence homology. GlyT1 presents four isoforms arising from alternative splicing and alternative promoter usage (1a, 1b, Ic and 1d). Only two of these isoforms have been found in rodent brain (GlyT1a and GlyT1b). GlyT2 also presents some degree of heterogeneity. Two GlyT2 isoforms (2a and 2b) have been identified in rodent brains. GlyT1 is known to be located in CNS and in some peripheral tissues, whereas GlyT2 is specific to the CNS, primarily in the hindbrain and spinal cord (Zafra et al., 1995, J. Neurosci. 15:3952-3969). GlyT1 is expressed in glia and neurons, and it is found to be located at glutamatergic synapses (Cubelos et al., 2005, Cereb. Cortex 15:448-459).
Glycine transporter inhibitors are suitable for the treatment of neurological and psychiatric disorders. The majority of diseases states implicated are psychoses, schizophrenia (Armer R E and Miller D J, 2001, Exp. Opin. Ther. Patents 11: 563-572), psychotic mood disorders such as severe major depressive disorder, mood disorders associated with psychotic disorders such as acute mania or depression, associated with bipolar disorders and mood disorders, associated with schizophrenia, (Pralong E T et al., 2002, Prog. Neurobiol., 67:173-202), autistic disorders (Carlsson M L, 1998, J. Neural Trans. 105:525-535), cognitive disorders such as dementias, including age related dementia and senile dementia of the Alzheimer type, memory disorders in a mammal, including a human, attention deficit disorders and pain (Armer R E and Miller D J, 2001, Exp. Opin. Ther. Patents, 11:563-572). Thus, increasing activation of NMDA receptors via GlyT1 inhibition may lead to agents that treat psychosis, schizophrenia (positive, negative and cognitive symptoms), dementia and other diseases in which cognitive processes are impaired, such as attention deficit disorders, Alzheimer's disease, or other neurological and psychiatric disorders.
All these concepts to medicinally benefit from the inhibition of GlyT1 are of high interest, in particular with respect to cognitive impairment associated with Alzheimer's disease or Schizophrenia.